Standard model flavor from an $SU(2)$ symmetry

TL;DR

This paper introduces a model where an $SU(2)$ symmetry explains the flavor structure of the standard model, predicting small fermion masses, mixing patterns, and CP violation consistent with observed phenomena.

Contribution

It proposes a new $SU(2)$ flavor symmetry framework that naturally accounts for fermion mass hierarchies, mixing angles, and CP violation in both quark and lepton sectors.

Findings

Predicts small light fermion masses and quark mixing angles.

Explains suppression of flavor-changing neutral currents.

Forecasts large CP violation and specific neutrino mass hierarchy.

Abstract

We propose that the flavor structure of the standard model is based on a horizontal $SU(2)$ symmetry. It generically predicts (i) a parametrically small mass for the lightest charged fermions, (ii) small mixings in the quark sector, and (iii) suppression of flavor-changing neutral currents. Supplemented with the assumption of a strong hierarchy between the second- and third- generation masses, it also predicts (iv) a large $CP$-violating phase in the quark sector. Only Majorana neutrinos allow for large mixings in the lepton sector. In this case, this framework further predicts (v) near-maximal $\theta_{23}^l$, (vi) a normal hierarchy of neutrino masses, and (vii) large $CP$ violation in the lepton sector.